Cast cable connections have been known in the prior art. Such systems have the advantage that they can be easily fabricated in the field at the place of the cable connection. However, where an increased resistance to fire is required, such cable connections have, up to now, not been usable. For example, plastic mold bodies typically will melt when exposed to fire, such that the resinous filler typically contained within the mold body becomes exposed. Because of the required castability of such filler resins, they typically can be provided only with limited resistance to fire and will be destroyed relatively quickly. Accordingly, in areas where fire resistance is of extreme importance, cables that are used therein are provided with fire resistant covers thereover, without the use of cast cable connections. This requires an increased usage of special and expensive cables. If a placed cable is damaged, typically excessively long cable sections must be exchanged in their entirety. Accordingly, a large inventory of such expensive special cables must be maintained.
Plastic materials having increased fire resistance are known in the art in numerous versions. Only a few of these plastics, however, are suitable for use with electrical systems, and especially so relative to cast cable connections. With the exception of a few plastics which are self-extinguishing because of a high halogen content therein, typical plastics are flammable and will in fact support combustion. Examples of self-extinguishing plastics include polyvinylchloride and polytetrafluoroethylene. To eliminate this noted disadvantage relative to most plastics, fire retardant additives are typically included therewith. The most commonly used are halogen-containing, phosphorous-containing and antimony-containing combinations. When exposed to flame, the corresponding acids are released by such compositions, which can then thus prevent continued burning.
There is extensive patent literature discussing this concept, examples of which include DE-OS No. 15 69 123, wherein antimony chloride is taught to be capable of acting as a fire retarding additive, and also DE-OS No. 14 94 922, wherein phosphene and phosphoric acid combinations are suggested.
However, it is well known that the acids released as flame protecting or retarding agents can provide corrosive combinations such that electrical and electronic equipment, including cables, can be damaged or destroyed. Furthermore, it is known that flame-retarding plastics can develop a considerable quantity of smoke due to the effect of fire or flame thereon, which can prevent extinguishing and salvage operations. Also, it has been more recently determined that the combustion products from flame-resistant plastics are toxic.
These disadvantages are taught to be overcome in DE-OS No. 27 39 429 by including within the plastic an inorganic magnesium combination, an alkali chloride and an inorganic zinc or vanadium combination. In this case, not only are zinc and vanadium combinations expensive, but considerable concentration of alkali chloride is required to arrive at a desired level of flame retardency. Also, such materials are typically undesirable in electrical equipment. In DE-AS No. 17 69 312, the use of borate as a flame retarding additive is disclosed. Although borates do not generate acids, the flame retardation available through their use is relatively low, such that the additional use of other fire retardant additives, such as antimony oxide, becomes necessary.
Finally, as disclosed in DE-OS No. 28 09 294, a halogen-free flame retardant additive, namely aluminum hydroxide in combination with magnesium carbonate, can be utilized together with copolymers of polyolefins and synthetic rubber. However, when used in such plastic materials, the required quantities of such additives are rather high, and same can be uniformly combined only through equipment such as rubber mills.
Accordingly, cast cable connections having sufficiently high resistance to fire have been unavailable.